1. Field of the Invention
The present invention relates to a fluorescent gas analyzer for analyzing gases such as SO.sub.2 and the like by the fluorescence method; in particular, the present invention relates to a fluorescent gas analyzer which is operated in a pulse mode.
2. Description of the Prior Art
In prior art fluorescent gas analyzers of the pulse mode type, a gas electric discharge flashtube, which is used as a light source, is operated in its pulse mode, and radiant energy of a first wavelength range is applied to a sample placed in a sample chamber. Fluorescent radiant energy of a second wavelength range, which is emitted from the sample due to the application of the radiant energy of the first wavelength range to the sample, is detected by means of an optical detector. The detected electric signals are accumulated in a capacitor during the time period when the flashtube emits the fluorescent energy of the first wavelength range (said time period hereinafter referred to as the period of duration of a flash). The accumulated (i.e.--integrated) voltage of the capacitor is discharged through an electric resistance during the time period when the flashtube has stopped emitting the radiant energy of the first wavelength range (said time period hereinafter referred to as the intervals between flashes). The integrated voltage accumulated in the capacitor is held in a sample and hold circuit as a sample voltage at the time when the flashtube stops emitting the radiant energy of the first wavelength range (said time hereinafter referred to as the flash completion time), and the sample voltage is output through a low-pass filter as a continuous signal which substantially follows the sample voltage. Thus, according to such prior art analyzers, a continuous measurement is possible even when the analyzer is operated in the pulse mode. In addition, the prior art analyzers have an advantage in that an accurate and reliable gas analysis is possible, except for the influence caused by fluctuations in the output of the light source, the deterioration thereof and the like, because the integrated voltage which is accumulated by the capacitor is the voltage value which responds to the radiant energy of the second wavelength range emitted from the sample.
It is, however, inevitable that the light source deteriorates and has fluctuations in its strength when used in a fluorescent gas analyzer of the prior art type. Thus, the fluorescent gas analyzers of the prior art type have a disadvantage in that the fluctuation of the strength of the light source leads to fluctuations in the strength of the fluorescent radiant energy of the second wavelength range emitted from the sample and it thereby appears that the apparent concentration of gas is changed and as a result thereof, errors in the measurement occur. Furthermore, it is feared that the continuous measurement is meaningless in itself because these errors of measurement are apt to be increased in proportion to the progress of the deterioration of the light source during its long term operation.